In experiments directed by her owner, psychologist John Pilley of Wofford College in Spartanburg, S.C., Chaser demonstrated her grasp of the basic elements of grammar by responding correctly to commands such as “to ball take Frisbee” and its reverse, “to Frisbee take ball.” The dog had previous, extensive training to recognize classes of words including nouns, verbs and prepositions.

“Chaser intuitively discovered how to comprehend sentences based on lots of background learning about different types of words,” Pilley says. He reports the results May 13 in Learning and Motivation.

Throughout the first three years of Chaser’s life, Pilley and a colleague trained the dog to recognize and fetch more than 1,000 objects by name. Using praise and play as reinforcements, the researchers also taught Chaser the meaning of different types of words, such as verbs and prepositions. As a result, Chaser learned that phrases such as “to Frisbee” meant that she should take whatever was in her mouth to the named object.

Exactly how the dog gained her command of grammar is unclear, however. Pilley suspects that Chaser first mentally linked each of two nouns she heard in a sentence to objects in her memory. Then the canine held that information in mind while deciding which of two objects to bring to which of two other objects.

Pilley’s work follows controversial studies of grammar understanding in dolphins and a pygmy chimp.

It’s hard to know what a dog or other nonhuman animal is actually thinking about when responding to commands, comments dog researcher and psychology graduate student Krista Macpherson of the University of Western Ontario in London, Canada. Debate about whether these animals understand that the meaning of commands rests on abstract rules will continue with Chaser’s behavior, in her view.

Chaser started sentence training at age 7. She stood facing a pair of objects she knew by name. An experimenter would say, for instance, “to ball take Frisbee.” In initial trials, the experimenter pointed at each item while saying its name.

After several weeks of training, two experiments conducted in Pilley’s living room tested Chaser’s grammar knowledge. A college student sat with the dog facing two pairs of objects. Chaser had to choose an object from one pair to carry to an object from the other pair. The student read commands that included words for those objects. Only some of those words had been used during sentence training, including “to sugar take decoy.” To see whether Chaser grasped that grammar could be used flexibly, Pilley had the student also read sentences in the reversed form of “take sugar to decoy.” In 28 of 40 attempts, Chaser grabbed the correct item in her mouth and dropped it next to the correct target.

Another experiment tested Chaser’s ability to understand commands when she couldn’t see the objects at first. Pilley stood at the end of a bed where Chaser sat facing him, with two objects behind her at the other end of the bed. After hearing a command, Chaser turned around and nabbed one of the objects. She then ran to the living room and delivered the item to one of another pair of objects. She succeeded on all 12 trials.

Border collies achieve similar grammatical insights when working with farmers to learn sheep-herding commands, Pilley speculates. With enough training, other dog breeds could also get a paw-hold on grammar, he predicts.